1. Field of the Invention
The present invention relates to nonreciprocal circuit devices such as isolators and circulators used in high frequency bands including microwave bands, and the invention also relates to communication apparatuses incorporating the same.
2. Description of the Related Art
In recent mobile communication apparatuses such as cellular phones, with the miniaturization of the apparatuses, a demand for cost reduction has been on the increase. As a result, reducing the sizes and production costs of nonreciprocal circuit devices have also been strongly demanded. In order to satisfy such a demand for miniaturization and cost reduction, there is a nonreciprocal circuit device provided by the assignee of the present invention in Japanese Patent Application No. 9-252207. The nonreciprocal circuit device as an isolator has a structure in which a single-plate-type capacitor is used as a matching capacitor, which is disposed perpendicularly with respect to a surface to be mounted. That is, the isolator has the structure in which the capacitor is vertically disposed.
As shown in FIG. 10, in this isolator, a permanent magnet 3 is disposed on an inner surface of an upper yoke 2, which is fit on an lower yoke 8 to form a magnetic closed circuit. A terminal case 7 is placed on the bottom surface inside the lower yoke 8. Inside the terminal case 7 are disposed a magnetic assembly 15, three matching capacitors C1 to C3, and a terminating resistor R. The permanent magnet 3 applies a DC magnetic field to the magnetic assembly 15.
In the magnetic assembly 15, three central conductors 51 to 53 are electrically insulated from each other and intersected on the upper surface of a ferrite plate 55. Ports P1 to P3 formed at one end of each of the central conductors 51 to 53 are bent at 90 degrees, and a common ground plate 54 at the other end of each of the three central conductors 51 to 53 abuts on the bottom surface of the ferrite plate 55. In a developed view shown in FIG. 11, the central conductors 51 to 53 are mutually connected by being integrated at a central area, which is equivalent to the ground plate 54, from which the central conductors 51 to 53 are outwardly extended. The ground plate 54, which substantially covers the bottom surface of the ferrite plate 55, is connected to the bottom wall 8b of the lower yoke 8 via a through-hole 7c of the terminal case 7.
In the terminal case 7, input/output terminals 71 and 72, and ground terminals 73 are insert-molded. One end of each of the terminals 71 to 73 is exposed outside the terminal case 7, and the other end thereof is exposed on the inner side wall of the terminal case 7. The matching capacitors C1 to C3 are disposed on the inner side walls of the terminal case 7 in such a manner that the electrode surfaces of the matching capacitors C1 to C3 make at angles of 90 degrees with respect to the upper and lower main surfaces of the ferrite plate 55. The ports P1 to P3 of the central conductors 51 to 53 are connected to hot-side electrodes of the matching capacitors C1 to C3. In addition, the ports P1 to P3 are connected to the input/output terminals 71 and 72 exposed on the inner side walls of the terminal case 7. Cold-side electrodes of the matching capacitors C1 to C3 are connected to the ground terminals 73 exposed on the inner side wall of the terminal case 7. One end of the terminating resistor R is connected to the hot-side electrode of the matching capacitor C3, the other end thereof is connected to the ground terminals 73. These components are electrically connected by soldering.
In the above conventional isolator, after the magnetic assembly 15 is incorporated into the terminal case 7, the matching capacitors C1 to C3 must be inserted between the ports P1 to P3 and the ground terminals 73 on the inner side wall of the terminal case 7 while vertically standing the matching capacitors C1 to C3. In addition, the electrodes of the matching capacitors C1 to C3 need to be connected to the ports P1 to P3 and the ground terminals 73 by soldering.
However, due to the miniaturization of the isolator and the components constituting the isolator, it is difficult and time-consuming to insert the small matching capacitors C1 to C3 in such narrow spaces between the ports P1 to P3 and the terminal case 7. Furthermore, since the ports P1 to P3 of the central conductors 51 to 53 need to be bent at right angles in advance, variations in the angles at which the ports P1 to P3 are bent can lead to unsteady soldering of the ports P1 to P3 to the matching capacitors C1 to C3. In addition, due to variations occurring in the state in which the magnetic assembly 15 is incorporated, the distance between the ports P1 to P3 and the ground terminals 73 is also varied, with the result that soldering the ports P1 to P3 to the matching capacitors C1 to C3 can be stabilized. Furthermore, with solder flowing out in the soldering process, the hot-side electrodes of the matching capacitors C1 to C3 and the cold-side electrodes thereof are short-circuited, thereby causing reduction in yields.
Accordingly, it is an object of the present invention to provide a highly reliable nonreciprocal circuit device into which matching capacitors can be easily incorporated, and a communication apparatus using the same.
To this end, according to one aspect of the present invention, there is provided a nonreciprocal circuit device including a ferrite plate having a first main surface and a second main surface, the ferrite plate being adapted to receive a DC magnetic field applied by a permanent magnet; a ground plate made of a conductive plate; a plurality of central conductors integrally extended from the ground plate, an end portion of each of the central conductors defining a port; a plurality of capacitor-connecting terminals integrally extended from the ground plate; and a plurality of matching capacitors, each having an electrode formed on each main surface thereof; wherein the ground plate abuts on the second main surface of the ferrite plate, and the plurality of central conductors are electrically insulated from each other while being extended along the side surfaces of the ferrite plate and mutually crossing on the first main surface of the ferrite plate; the plurality of matching capacitors are disposed between the ports of the central conductors and the plurality of capacitor-connecting terminals to be electrically connected to the ports and the terminals; and at least one of the matching capacitors are disposed in such a manner that the electrode surfaces thereof define an angle from 60 to 120 degrees with respect to one of the main surfaces of the ferrite plate.
In the above arrangement, the matching capacitors are connected between the central conductors and the capacitor-connecting terminals integrally placed with the central conductors disposed on the ferrite plate. As a result, the matching capacitors integrated with the central conductors and the ferrite plate can be regarded as a part of a single unit. This arrangement permits incorporation of the matching capacitors to be facilitated.
In addition, the above nonreciprocal circuit device may further include an insulator for preventing an outflow of solder disposed in the vicinity of each of the parts where the plurality of capacitor-connecting terminals are connected to the plurality of matching capacitors and in the vicinity of each of the ports of the plurality of central conductors. With this arrangement, since the outflow of solder is controlled when soldering the matching capacitors, for example, this prevents hot-side electrodes of the matching capacitors and cold-side electrodes thereof from being short-circuited.
In addition, the above nonreciprocal circuit device may further include an insulator for preventing a short circuit disposed at each of the parts where the central conductors are close to the matching capacitors. With this arrangement, the central conductors are not short-circuited with the matching capacitors even when the central conductors contact with the matching capacitors due to an external force or variations in assembly.
Furthermore, according to another aspect of the present invention, there is provided a communication apparatus including the above nonreciprocal circuit device. The communication apparatus of the present invention can be produced at low cost with high reliability.